


sine/cosine

by GhostyKitty



Series: Haikyuu Oneshots [7]
Category: Haikyuu!!
Genre: Enemies to Friends to Lovers, F/M, Fluff, i think
Language: English
Status: Completed
Published: 2020-11-28
Updated: 2020-11-28
Packaged: 2021-03-10 06:53:28
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,391
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/27750052
Author URL: https://archiveofourown.org/users/GhostyKitty/pseuds/GhostyKitty
Summary: when he first met you, Kuroo Tetsurou didn't realize how much you'd grow on him.
Relationships: Kuroo Tetsurou/Reader
Series: Haikyuu Oneshots [7]
Series URL: https://archiveofourown.org/series/1788043
Kudos: 63





	sine/cosine

The tailored suit jacket feels just a little too snug around his shoulders right now. Or maybe it’s his nerves, making him breathe just a little deeper in an attempt to keep his cool. But he can never truly keep his cool around you. There’s so much he wants to tell you, so much he wants to say, but there’s a strict schedule he needs to follow, and he’s not quite sure his notes are in the right order either. 

Nevertheless, he pulls them out of his suit pocket, thankful that his hands are a tad bit clammy making it easier to flip through them. Coughing a little, he tries to clear his throat of any anxiety. He takes one last deep breath in before opening his mouth. “When I first met you, I thought we were a pair of intersecting lines. Fated to meet just once and then never again.” 

\---

The first thing he did after he put on his uniform was loosen the tie. Just a little bit. Not enough to look sloppy or get him in trouble with any teachers. His mountain range of a bedhead was more likely to do that. Kuroo Tetsurou, first year student at Metropolitan Nekoma High School, just wants to breathe. 

As usual, he met Kenma outside and they walked to the train station together. His legs guided him through the crowd, trained reflexes keeping him on his toes. He was about to step onto the train when suddenly, “Kuroo,” the mellow voice of his childhood friend broke him out of his zone. “Aren’t you supposed to take the other train?” 

“Oh shit.” 

The first year glanced down at his phone, sucking in a deep breath when he saw that the train he was supposed to take was arriving in two minutes. That’s enough time to get to the other platform. Right? He broke out into a mad dash the moment the coast was clear, only slowing down when he turned corners or traversed stairs.

Despite his attempts to prevent any accidents from occurring, Kuroo was bound to slip up at some point. And he did. All it took was one glance down at his cellphone and he was on the ground before he could even register the throbbing pain in his tail bone.

A groan left his lips as he slowly tried to get up. 

“Watch where you’re going!”

Kuroo’s brow twitches in irritation as he looks up to see you, a frustrated girl scrambling to stuff, what appears to be, holiday homework into a worn canvas messenger bag. “I could say the same to you,” he grumbled, hissing as pain shot through his backside. He could already imagine the giant bruise making practice an absolute hell. The strained noise made you glance over with raised eyebrows. 

With a huff you swiftly shoved all your papers into your bag and stood up to dust yourself off. “Need help?” you asked, offering a hand to help him up.

“Nah, I’m fine,” Kuroo brushed it off and got up on his own, grumbling as he double checked his bag and pockets to make sure nothing came tumbling out. 

“Right,” you murmured as you glanced down at the watch on your wrist. Curses tumbled out of your mouth as you began rushing your steps to catch the train, but not before turning around to tell the disgruntled bed head, “watch where you’re going next time!”

Kuroo clicked his tongue at your warning before looking down at his phone. Suddenly it was his turn to curse at the sight of the notification that the train would be arriving in less than one minute. 

He made sure he put his phone in his pocket before he started running.

\---

“It was when we met a second, third, fourth, fifth time that I knew you’d be staying in my life. At the time, I didn’t really want you to because we’d just left an absolutely stunning first impression on each other,” he teases. “And it wasn’t the exact way that I would have wanted you to stay in my life either,” an indignant squawk emerges from behind him, “but that doesn’t matter now.”

A few chuckles emerge from the crowd of friends and family. 

\---

Kuroo’s brow twitched with annoyance as he gazed down at the familiar face of the libero from the team that struck his down on the path to nationals his last year of junior high. Piercing brown eyes stared back at him with slight confusion mixed with defiance, only fanning the flames of irritation in his chest. Kuroo’s chin tilted up as he sized up the other first year boy. Brown eyes narrowed back.

A little voice in the back of his head whispers that they’re gonna get along as well as dogs and cats.

Yaku Morisuke. Everything from his stature to his temper appeared to be short. However, his skill as a libero was unquestionable. From the way he moved around to the way his eyes could analyze and understand the other side of the net in only a few seconds, Kuroo was sure that in a few years time he’d be much more experienced. 

He told himself to begrudgingly accept that this former rival was now a teammate if only for the sake of making it to nationals. Yet, it was only the third day of practice and Kuroo was finding that his resolve to somehow befriend the shorter first year was slowly crumbling. 

The true test, however, arrived in the second week of school. 

Practice was going on as usual. Running, receiving, blocking, spiking. That day, due to their unfortunate lack of a manager, he was on water duty too. The water fountain was a little out of the way, so it was decided amongst the upperclassmen that it was much easier to dump the job on a different person every practice. Fortunately, the fountain on this side of the school ran just a little more aggressively, so filling these things up never took that much time. 

Just as he finished screwing the top of the last bottle back on, the sound of shoes scraping against the ground approached him from behind. “Sorry to bother you, but can I ask for some directions?” 

Kuroo’s brow twitched with annoyance as he placed the bottle in the carrier and turned around to see you, the girl from the train station. “Well this is an interesting coincidence isn’t it?” he says, trying his best to keep a pleasant expression. There was a tense moment of silence between the two of you as the situation sank in. 

“Ah!” you yelled, breaking the silence. “You’re the old guy from the train station!”

“What?!” Kuroo sputtered at your exclamation. “Who are you calling old?”

“Definitely could have fooled me. I mean you certainly sounded like one at the train station,” you said, a lighthearted snicker following the statement. 

“Well, I’ll have you know that I’m still in my first year here, and I’m on the volleyball team,” Kuroo boasted, tilting his chin up in an attempt to stretch the height he was blessed with. Your eyebrows rose in surprise.

“Oh? My friend is on the team here too,” you said, lifting a hand to your chin. 

“Really?”

“Yeah, he’s a libero.” Kuroo’s brow twitched again. 

“I’m sorry could you repeat that?.”

“What, too tall to hear what’s being said down here?” you asked with a smug grin tugging at your lips.

“No,” Kuroo retorted, “just wanted to make sure you aren’t insane or something.” Your confident expression dropped into one of irritation as your mind struggled to formulate a response. 

“Oi! Kuroo! What’s taking you so long?” Your savior emerged from around the corner in all his 165 centimeters of glory. Kuroo wanted to groan. Instead he turned around with a forced smile. 

“Yaku, do you know this kid?” he asked, tilting his head to gesture to you.

“I’m not a kid!” you scoffed. “I’m in my third year of junior high!”

“Oh, really,” Kuroo grinned, “could have fooled me.” 

\---

“We definitely had our differences at first, and I’m sure most of the people here today have been witness to at least one of our squabbles. But those squabbles are what strengthened our bond and brought us closer together.”

\---

You were introduced to everyone as Yaku’s childhood friend. 

As next door neighbors only separated by a year, it was inevitable that you’d become friends. Perhaps it was the convenience of living next to each other, or the fact that you ended up going to the same elementary school, but the friendship the two of you had cultivated over the years was substantial enough to affect which high school you wanted to attend. 

This was also why, for the next year, you’d periodically appear at the gym doors with food in hand or a message for Yaku from his mother. Every encounter Kuroo had with you led to some form of… debate. Petty squabble would be a more fitting term. Topics ranged from mundane things like the weather to more complex issues like which fast food restaurant chain has the best fries.

While Kuroo did find it fun to provoke you at times, seeing how nervous you were on the first day of your first year in high school, he decided to spare you the needling. Kenma was standing next to him, absorbed in whatever new gacha game had recently come out, trying his best to avoid interaction as much as possible. This meant Kuroo wouldn’t be able to escape to the stable familiarity that was his own childhood friend. He had to have a civilized conversation with you and Yaku.

“-oh yeah, Miyano-sensei is super strict about exam answers and he’ll dock points if you do things just a little different from how he teaches it.” Yaku said, trying his best to prepare you to deal with some of the teachers at the school. 

“Mori that’s the fourth mean teacher you’ve told me about,” you groaned, “aren’t there any nice ones you can tell me about before I start regretting my first major life decision?” 

“Yamashita-sensei is pretty nice,” Kuroo chimed in. “She teaches English and she gets really enthusiastic when people ask her questions. Something about ‘encouraging the youth to participate on the world stage.’” 

“But Kuroo was in class 2 last year, so the teachers were probably…” Yaku paused to think of the right words to use.

“More on their level?” you suggested with a giggle. Yaku hummed and nodded in agreement. 

“Well, I’ve been bumped up to class 4 this year which is college prep,” Kuroo said, his chin tilted up and chest puffed up a bit to boast.

“I’ve been placed in class 5,” you said. Your voice seemed so much smaller, the confidence you put on display just moments earlier having dissipated into the morning air. “Not quite sure what they were thinking. It’s not like I did absolutely flawless on the entrance exam...” You trailed off with a sigh, brows furrowed at the thought of the work you’d be required to do. 

“You’ll get used to it,” Yaku said, patting your shoulder in an attempt to cheer you up. “And if you ever need help don’t be afraid to ask us!” 

“Okay.”

Despite all the anxiety that had accumulated regarding the difficulty of the classes, you found yourself doing quite well. At least, well enough. Among your fellow peers, you considered your grades to be relatively average. You joined a club, made new friends, and still stopped by the Boys Volleyball Club to say hi. 

Then midterms rolled around.

Kuroo was called to the teacher’s office two weeks later. FIlled with nerves, he tugged the knot of his tie down, giving himself more room to breathe. He was pretty confident in his academic capabilities. He couldn’t have done that bad right? 

He took a deep breath in and knocked on the door, announced his arrival, and stepped in. 

To his surprise, you were standing there, being lectured by Miyano-sensei. Kuroo nearly grimaced with how loud he was. Clutched in your hands were a slim stack of papers, crinkled from your tight grip. Even if it’s difficult to get along with you sometimes, he wouldn’t wish the wrath of Miyano on his worst enemy.

“Ah, Kuroo,” the guidance counselor called him over, “I need you to update your emergency contact information.” The second year breathed a sigh of relief before he nodded. With as quiet steps as possible, Kuroo made his way over to the guidance counselor’s desk to look over the paperwork. As he walked by, he could swear that you flinched. 

Just as Kuroo finished going through the phone numbers and addresses, Miyano finished his tirade. The two of you stepped out of the office at the same time and a tense silence settled between you. He contemplates saying something, but decides against it. You probably don’t want to get any advice from a guy you dislike after being lectured to hell and back in front of him. 

He loosens the tie around his neck a little more. 

“Please don’t tell Mori,” your voice was uncharacteristically small. “If he finds out, the chances my mom finds out will skyrocket. And I really don’t want to hear it from my mom after that.”

Kuroo cleared his throat a little, lowering his voice to match yours. “I won’t tell.” He tries to spot your face out of the corner of his eye. 

“Thanks,” you said, turning away. “I appreciate it.” You took a step to leave in the opposite direction as him, shoulders slumped and maybe even trembling a bit. Kuroo moved before he could register what he was doing. 

“I can help you, if you want.” You stopped in your tracks at the sound of his voice. “I might not have been in the college prep class, but I still had Miyano. I-” Kuroo’s voice catches in his throat “-I can lend you my notes from last year.” 

Your reply was a shaky but simple, “Sure.”

Meeting in the library on the days he didn’t have practice became routine. For about an hour the two of you would tone down the urge to needle each other for the sake of your grades. You even started getting along outside of these study sessions. There was less tension and fewer debates in the morning. Volleyball club visits were more fun. Kuroo was having a good time.

That was up until you started showing up late. 

At first, it was only a couple of minutes. Nothing too drastic. It’s not like either of you were perfectly on time every single day. But then just a few minutes began to grow until you were consistently ten, fifteen, twenty minutes late.

One day, Kuroo found himself standing outside the library like some housewife waiting for her salaryman husband to come home from a late night of drinking with his coworkers. Every few seconds he was either checking his watch, running a hand through his hair, or tapping his foot with his arms crossed. You should have just texted him if you were going to ditch. He could be hanging out with the rest of the volleyball team right now instead of wasting his time waiting here. 

The sound of frantic footsteps rounded the corner and caught his attention. Kuroo shifted his irritated glare to see if it was you, only for his ire to grow exponentially when it wasn’t. He glanced down at his phone, clicking his tongue when it revealed you hit a new record of at least thirty minutes.

A new set of footsteps rounded the corner. “Kuroo-” 

“Listen,” the second year snapped, “I get that you’re not the biggest fan of me, but please don’t waste my time like this.”

“Wait, Kuroo I’m sorry,” you scrambled to increase your pace to catch up to him. “I really need your help with Miyano’s class-”

“How can you say that when you’re late to like, 80% of our meetings?” 

“Listen-”

“I can’t believe I thought we were actually starting to become friends-” A hand grabbed onto his school bag.

“Kuroo, just listen to me please!” The black haired boy spun around with narrowed eyes and clenched fists. 

“I’ll give you thirty-two seconds to explain yourself,” he grumbled. 

“Wha-” you scoffed, “thirty-two seconds isn’t enough!”

“Tick tock,” he said with his chin tilted up, looking down at you with annoyance growing in his eyes.

“Okay fine,” you mumbled. “I need you to follow me and not tell anyone about this.” Kuroo raised one eyebrow, inclining his head as you swiftly turned around and started walking down the hallway. You paused to look back when you didn’t hear him follow. “Do you want your explanation or not?” 

Kuroo clicked his tongue at your petulant tone. Couldn’t you just spit out some excuse like always?

“It’s much better than words I promise.”

With a sigh, Kuroo reluctantly began to trail after you while dragging his feet in a petty attempt to slow you down. However, you didn’t seem to mind pausing whenever you got more than ten feet ahead of him. Gradually, as you led him through the school, his frustration morphed into curiosity. Just where were you taking him?

You led him through the gates of the school and around the outside of the fence that surrounded the sports fields. Then you arrived at your destination: the old construction site. The school often discouraged students from coming here, mostly out of fear someone would step on a rusty nail. What could you want to show him here?

WIth his curiosity really truely piqued, Kuroo followed you intently, raising a brow when you crouched down near one of the old steel pipes left behind. It was then that he heard the tiny squeaks. 

“I’m back!” you greeted, “I’m sorry we interrupted your nap.” Kuroo’s eyes widened as tiny squeaks shifted into little yips of excitement. You picked something up and turned to show him. His breath was caught in his throat as he took in the sight. It was a small, black and white, curly furred puppy. It looked young, but it was definitely at least a month old. 

“Where? Why?” Kuroo asked. His brain had short circuited. Your subsequent laughter startled some of his brain cells awake. 

“Here, you hold him,” you said, stifling your chuckles. And just like that Kuroo’s brain shut down again. He couldn’t refuse those dark, wide eyes, filled with excitement and the little tail wiggling back and forth. So he hesitantly accepted the pup into his arms, scared that if he moved the wrong way he’d drop the little furball. 

“I found him abandoned near the school,” you explained. “I can’t take him home because my parents definitely won’t let me keep him, and I didn’t want to just take him to the pound.” Kuroo hummed, watching as the puppy settled into his arms. “I didn’t really know what else to do, and I couldn’t ask Yaku because he doesn’t like dogs. So I’ve been keeping him here and feeding him leftovers from lunch.” 

“I can try to take him.” The words leave his mouth before he can really process what he said. Your sharp inhale along with eyes glimmering with hope had him backpedaling as fast as possible. “I mean, I can’t make any promises obviously, but I can ask around my neighborhood, see if anyone is willing to take him in.” 

The way your face lit up was worth it. Maybe that was when he started to fall.

\---

“On that day, I resolved to make you smile as much as possible. And, not to toot my own horn or anything like that, but I think I’ve done a pretty good job!” He leans forward with a teasing grin on his face, making your own painted lips purse to hold in the laughter bubbling up from your stomach. “And I’ll do my best to keep doing so.”

\---

Kuroo was entranced.

Conversations at the train station platform were much more pleasant. He found himself looking forward to your visits to the volleyball club, to seeing you smile and laugh. The study sessions in the library were gradually growing in length. 

It was during these study sessions that he decided to start a new ritual with you. After scribbling something down on a scrap piece of paper, Kuroo tapped your arm and slid it over.

Why did the bike fall over? It was two tired (๑ゝڡ ◕๑)

Seeing you smile and laugh was worth the glare from the librarian.  
When finals week came around, club activities were suspended so everyone could focus on their exams. Studying together in the library was nothing new, but for one whole week, Kuroo got to see you for several hours after classes ended. And he most certainly wasn’t going to let this chance slip through his fingers.

“Psst.” Kuroo tapped your arm before sliding a piece of paper over. 

_What kind of pictures do eukaryotes take best? CELLfies (･ω <) -☆_

You couldn’t stifle your laugh in time and got scolded by the librarian. “I’m sorry,” you whispered, “I’ll do my best to stay quiet.”

The next day, Kuroo did the same thing.

_What do you call a cow with two legs? Lean beef (ര௰ര)_

While you did manage to stay quiet this time, the choked sounds that came from you earned some irritated looks from your fellow students. “Kuroo! You can’t keep doing this!” you whispered, trying not to let the smile on your face show through. The second year simply went back to his work with a smug grin on his face.

Over the next few days Kuroo would proceed to do the same thing time and time again. 

_What do you call a cow with no legs? Ground beef (•̀⌄•́)✧_

_There was a noodle that wasn’t like the rest. He was an impasta ฅ(*°ω°*ฅ)_

_What kind of shorts do clouds wear? Thunderpants ꒰ *๑•ૅʖ̫•́๑꒱_

For every joke he slid over to you, Kuroo was rewarded with the beautiful sight that is your smile. He couldn’t get enough of it. Unfortunately, he doesn’t have an endless supply of jokes, so he eventually had to turn to other sources for help.

“Kenmaaaaaa,” the second year pleaded, “just help me think of one more, just one more!” 

The first year’s eye twitched as he looked down at his childhood friend sprawled out on the floor of his room, a plate of chestnuts sitting between them, wracking his brain for ideas. “Kuroo, why don’t you just ask her out?” The second year flushed and immediately sat up. 

“W-what do you mean?” 

Kenma put his phone down and raised an eyebrow. “If you asked her out you wouldn’t have to pester me every day for new jokes.” Kuroo was silent for a few seconds. He looked down at the list of jokes in his phone. He ran a hand through his hair, sat up straight, and looked Kenma in the eye.

“Will you help me come up with a pick up line then?” Kuroo asked, a mischievous grin tugging at his lips. Kenma clicked his tongue and flopped back onto his bed, ignoring the complaints that followed. “Hey I just need you to tell me if you think it’ll work!”

“Kuroo, I’m pretty sure she’d say yes regardless of what pickup line you use.”

“Then help me make it as terrible as possible.”

“...fine.”

_Are you a Castanea? Because whenever I see you my chest goes nuts._

You started going out the next day.

\---

“You’ve given me countless chances to learn and grow, and I can’t thank you enough for that. And each day we spend together, I find more reasons why I want you to be the one I spend the rest of my life with.” A gentle silence settles over everyone as they take in his words. 

The officiant opens his mouth to move the ceremony forward, but before he can even utter a single word, Kuroo keeps talking with gusto. “Which is why I’d like to compare us to a pair of glorious sine and cosine waves, with an ever increasing frequency so that we intersect continuously and for the rest of forever.”

On the white projector screen used to display a series of pictures of the soon-to-be-married couple prior to the ceremony, is an image of the sine and cosine waves Kuroo is referring to. The officiant gazes up at the screen with his mouth just slightly ajar. This most definitely did not happen during the rehearsal. 

A bright red dot appears, swishing to and fro as the groom explains just what everyone is looking at. “So these, as everyone can see, are two functions, sine and cosine. And while they start out sort of intersecting at a slow rate,” he pauses to click on the button that’s supposed to lead to the next slide. It doesn’t change. Kuroo sighs and taps the laser pointer against his hand before trying again. He clicks his tongue in disappointment when the slide remains the same. “Hey, uh, Kenma,” he calls out to the projector booth, “can you change the slide for me?” The slide on display changes to one that shows more of the positive x-axis, and more of the oscillating sine and cosine waves. “Thanks! Right, as you all can see, these two lines end up intersecting, for basically the entirety of the x-axis, and-”

A choked sound interrupts him. 

Kuroo’s head whips around to see you hunched over, hand covering your mouth, and shaking. He glances at your maid of honor, who’s glaring daggers at him and patting you on the back. Did he just fuck up?

Suddenly, your tiny gasps turn into snorts, which shift into a laughter (or is it sobs?) so strong you’re bent over and clutching your stomach. “Uh, babe?” The entire room is silent, save for the sound of you cackling uncontrollably.

The laughter dies down just a little, enough for you to stand up straight and look at him. You take a shaky step forward, gently place your hands on the lapels of his suit, and tug him forward. “Just marry me you dork.” Kuroo grins widely.

“Gladly.”

Insp: https://i.redd.it/m1w6j2il5om51.jpg

**Author's Note:**

> come chat with me on tumblr @catharsisbabey!


End file.
